1. Field of the Invention
An internal combustion engine omits the fuel ration from a fraction of its combustion chamber cycles. The pattern of fuel ration inhibition is selected primarily to control the average engine output torque, and secondarily to control transmission of vibration from the engine to its environment.
2. Prior Art
Gasoline engines generally require some means of controlling their output torque, since the maximum available torque is not always wanted. The traditional method of controlling output torque is to throttle the air intake so that the engine operates at a reduced air pressure. The air intake pressure is then sensed and used in adjusting the ration of fuel for each cylinder cycle so that the fuel-air ratio is near its optimum value. Exact timing of spark ignition is also made to depend on the air intake pressure.
The air intake pressure affects many engine characteristics such as the amount of fuel needed, vaporization and mixing of the fuel with the air, charge stratification, charge ignition, rate of burning, detonation, heat transport to the wall, deposition of carbon, exhaust gas pressure, exhaust gas recirculation, piston blowby, crankcase ventilation, and atmospheric pollution. Thus a gasoline engine's performance is necessarily compromised if it must operate over a wide range of air pressure.
Methods of engine torque control which eliminate the need to heavily throttle the air intake are disclosed in U.S. Pat. Nos. 2,771,867, 2,875,742, 2,878,798, 2,919,686, 3,100,478, 3,181,520, 3,756,205, 4,103,655 and 4,040,395. These methods reduce engine output torque by inhibiting the ration of fuel in a fraction of the combustion chamber cycles. All of the engines in these eight disclosures use fuel injector valves. In the engines of the last disclosures, the valves are electrically operated and the fraction of fuel rations which is skipped is varied through the intervention of an electronic fuel injection inhibitor.
When the engine must be operated with an output torque well below its maximum possible value, the injection inhibitor can be set for partial output torque. Then heavy air throttling is not needed and the throttle can be kept near the point of peak engine efficiency.
Inhibited fuel injection in these engines tends to prolong the life of the exhaust valves and the exhaust pipe. Moreover, cylinder cycles with inhibited fuel injection tend to either oxidize or cool any hot carbon deposits within the cylinder, thus discouraging preignition. This action is particularly effective at low torque levels that tend to develop carbon deposits in conventional engines.
In engines with carburetors, fractional inhibition of fuel rations can be implemented by cutting off the air-fuel mixture to particular predetermined cylinders. Many engines using the principle have been built. Engines of this type are disclosed in U.S. Pat. Nos. 2,250,814 and 4,018,204 and in Popular Science, January 1977, page 70-72.
A difficulty with all of these engines having inhibited fuel rations is the uneven generation of power. This difficulty can be alleviated by using a rather heavy flywheel. Another difficulty is that these engines tend to vibrate excessively at low engine speeds.
If an internal combustion engine is not bolted down to a massive foundation, it tends to vibrate and to transmit its vibration to the environment. The forces producing vibration are classified as either gas forces or inertia forces. Of these, the inertia forces tend to increase in proportion to the square of the engine speed, and to be unaffected by fuel ration inhibition per se. The gas forces are approximately balanced, but they result in an uneven engine output torque, whose reaction on the engine tends to make the engine rock about an axis roughly parallel to the crankshaft axis. This engine rocking torque tends to be independent of engine speed, so that engine rock due to gas forces dominates at low engine speeds.
In order to reduce transmission of engine vibration to the environment, the engine is commonly mounted on a resilient support allowing it to rock, with a restoring couple giving it a natural rocking frequency lower than most engine frequencies. This arrangement works well at the higher engine speeds, but it may do more harm than good at a low engine speed for which a gas torque frequency coincides with the natural engine rocking frequency.
When an engine has a fraction of its fuel rations inhibited, the reduction of its average output torque is accompanied by an increase in some of its low frequency torque components. Thus at low engine speeds a considerable amount of mechanical vibration may be transmitted from an inhibited engine to its environment. If there is a flexible drive train between the engine and its load, excessive oscillation may develop in this drive train, especially at low engine speeds.